Preparation method of solar cell

Abstract

The invention discloses a preparation method of a solar cell, which belongs to the technical field of solar cells and comprises the following steps of: selecting an N-type silicon substrate and performing double-sided texturing; performing boron diffusion doping on the front surface of the silicon substrate to form a P + doping layer and a borosilicate glass layer on the front surface, and forming a borosilicate glass layer on the back surface; removing the borosilicate glass layer on the back surface of the N-type silicon substrate, and carrying out alkali washing and polishing on the back surface of the N-type silicon substrate; forming a polycrystalline silicon layer and a polycrystalline silicon layer on the back and the front of the substrate; performing phosphorus diffusion on the polycrystalline silicon layer on the substrate; removing the phosphorosilicate glass layer on the front side, the borosilicate glass layer, the N + polycrystalline silicon layer and the borosilicate glass layer and the phosphorosilicate glass layer on the back side; depositing a front passivation layer and a front antireflection layer on the P + doping layer on the front of the substrate; electrode printing sintering is carried out on the front and back of the substrate; the reverse bias voltage applied by the first LECO process is 3-10V, and the reverse bias voltage applied by the second LECO process is 11-20V. And the black edge problem caused by overburning is reduced by increasing the LECO for the second time.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, and in particular relates to a method for preparing a solar cell sheet. Background Art

[0002] Battery EL black edge refers to the phenomenon that black areas appear at the edge of the battery during the electroluminescence test of the battery. This phenomenon mainly comes from the red area at the edge of the silicon wafer ingot. The red area refers to the low minority carrier lifetime area at the edge of the silicon ingot where impurities and defects are enriched. Battery EL black edge will affect the efficiency of the battery, but will not affect other battery properties. Battery EL black edge mainly affects the efficiency of the battery. Although the black edge itself does not affect other battery properties, it will reduce the conversion efficiency of the battery, thereby affecting the overall performance of the photovoltaic module. In addition, the black edge area may cause leakage problems, which in turn affects the long-term stability and safety of photovoltaic modules and systems.

[0003] At present, in the coating process of the production line, the silicon wafer is not tightly fitted with the boat blade of the graphite boat, which causes the silicon wafer to be wrapped during coating. The film thickness around the silicon wafer is relatively thick. After screen printing the slurry, the glass in the slurry fails to completely open the silicon nitride film layer during the sintering process due to the thick film thickness around the periphery. The normal bias voltage is applied during the LECO process to cause a high temperature, which causes the peripheral area to overburn, causing black edge abnormalities. The proportion of black edge abnormalities in the current production accounts for about 3% of the number of single crystal slices produced. Although the proportion of this part is not large, it has a great impact on the subsequent battery cell process. By optimizing the production process and improving production conditions, the formation of black edges can be effectively reduced, thereby improving the efficiency and stability of the battery.

[0004] The prior art discloses some patents for controlling the production process of single crystal black edges, among which the invention patent with the announcement number CN104389015A discloses a production process method for controlling the black edges of single crystals, including silicon material sorting process, silicon material cleaning process, silicon furnace material preparation process, crystal pulling process and cooling process. Although the problem of single crystal black edges has been controlled, the range of reducing the black edge rate is small.

[0005] In view of this, the inventor conducted in-depth research on this demand, which resulted in this case. Summary of the invention

[0006] In order to overcome the problem of a small reduction range of the black edge rate in the prior art, the present invention provides a method for preparing a solar cell, comprising the following steps:

[0007] Step 1: Select an N-type silicon substrate and perform double-sided texturing;

[0008] Step 2: Diffuse boron on the front side of the silicon substrate to form a P+ doping layer and a borosilicate glass layer on the front side and a borosilicate glass layer on the back side;

[0009] Step 3, removing the borosilicate glass layer on the back side of the N-type silicon substrate, and performing alkali cleaning and polishing on the back side of the N-type silicon substrate;

[0010] Step 4: forming a silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a polysilicon layer on the silicon oxide layer, and at the same time forming a polysilicon layer on the borosilicate glass layer on the front surface;

[0011] Step 5: Phosphorus is diffused into the polysilicon layer on the back side of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer on the back side and an N+ polysilicon layer and a phosphorus silicon glass layer on the front side;

[0012] Step 6: remove the phosphosilicate glass layer, the N+ polysilicon layer, the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side;

[0013] Step 7: sequentially depositing a front passivation layer and a front anti-reflection layer on the P+ doped layer on the front side of the N-type silicon substrate;

[0014] Step 8, depositing a back anti-reflection layer on the N+ polysilicon layer on the back side of the N-type silicon substrate;

[0015] Step 9: Electrodes are printed on the front and back of the N-type silicon substrate, and then sintered and light decayed to form metal electrodes;

[0016] Step 10: Perform two LECO processes to further sinter and optimize the contact. The reverse bias voltage applied in the first LECO process is 3-10V, and the reverse bias voltage applied in the second LECO process is 11-20V.

[0017] Furthermore, in the step 10, the laser power irradiated on the cell piece is 10%-40%.

[0018] Furthermore, in step 4, the thickness of the silicon oxide layer is 1-2.5 nm, and the thickness of the polysilicon layer is 120-180 nm.

[0019] Furthermore, in step five, the sheet resistance of the N+ polysilicon layer is 37-53Ω.

[0020] Furthermore, in step seven, the thickness of the passivation layer is 4-5 nm.

[0021] Furthermore, in the step eight, NH3 and SiH4 are introduced under vacuum conditions, and the thickness of the anti-reflection layer is 73-83nm.

[0022] Furthermore, in step nine, NH3 and SiH4 are introduced under vacuum, and the thickness of the anti-reflection layer is 75-85nm.

[0023] Furthermore, in the step 1, a nanoscale texture is formed on the front and back sides of the N-type silicon substrate.

[0024] Furthermore, in the step 2, BCl 3 gas is introduced when boron diffusion is performed on the front side of the N-type silicon substrate.

[0025] The beneficial effects produced by the technical solution of the present invention are as follows:

[0026] The LECO process is carried out twice during the production of solar cells. The first time, a bias voltage of 3-10V and laser scanning are applied. The temperature generated by the relatively small bias voltage is relatively low, and the temperature generated by the first scan can be used to further open the silicon nitride film layer. The second time, a bias voltage of 11-20V and laser scanning are applied to form a good ohmic contact. Since the silicon nitride film layer is further opened at the periphery, ultra-high temperature is not generated in the peripheral area, solving the problem of black edges caused by overburning. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] This embodiment performs two processes during the LECO process. The first process is to apply a bias voltage of 3-10V and laser scanning. Since the applied bias voltage is relatively small, the temperature generated is relatively low, and the temperature generated by the first scan can be used to further open the silicon nitride film layer; the second process is to apply a bias voltage of 11-20V and laser scanning to form a good ohmic contact. Since the silicon nitride film layer is further opened at the periphery, the peripheral area does not generate an ultra-high temperature, solving the black edge problem caused by overburning. The specific implementation is as follows:

[0029] A method for preparing a solar cell comprises the following steps:

[0030] Step 1: Select an N-type silicon substrate and perform double-sided texturing;

[0031] Step 2: Diffuse boron into the textured silicon wafer to form a P+ doping layer and a borosilicate glass layer on the front side and a borosilicate glass layer on the back side;

[0032] Step 3: remove the borosilicate glass layer on the back of the N-type silicon substrate by acid washing, and perform alkaline washing and polishing on the back of the N-type silicon substrate;

[0033] Step 4: forming a silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a polysilicon layer on the silicon oxide layer, and at the same time forming a polysilicon layer on the borosilicate glass layer on the front surface;

[0034] Step 5: Phosphorus is diffused into the polysilicon layer on the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer on the back side and an N+ polysilicon layer and a phosphorus silicon glass layer on the front side;

[0035] Step 6: First, use hydrofluoric acid to wash away the phosphosilicate glass layer on the front side of the N-type silicon substrate, then use sodium oxide solution to wash away the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally use hydrofluoric acid to wash away the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side;

[0036] Step 7: using ALD to sequentially deposit an aluminum oxide layer on the P+ layer on the front side of the N-type silicon substrate, and using PECVD to deposit a SiN layer on the aluminum oxide layer on the front side of the N-type silicon substrate;

[0037] Step 8: Using PECVD to deposit a SiN layer on the N+ polysilicon layer on the back of the N-type silicon substrate;

[0038] Step nine: Electrodes are printed on the front and back of the N-type silicon substrate, and then sintered and light-decayed to form silver electrodes.

[0039] Step 10: Perform two LECO processes to further sinter and optimize the contact. The reverse bias of the first LECO process is 3-10V, and the reverse bias of the second LECO process is 11-20V.

[0040] As a preferred implementation, the laser power irradiated on the cell in step 10 is 10%-40%.

[0041] As a preferred implementation, in step five, the sheet resistance of the N+ polysilicon layer is 37-53Ω.

[0042] As a preferred implementation manner, the thickness of the aluminum oxide layer in step seven is 4-5 nm.

[0043] As a preferred implementation manner, in the step eight, NH 3 and SiH 4 are introduced under vacuum conditions, and the thickness of the SiN layer is 73-83 nm.

[0044] As a preferred implementation manner, in step nine, NH3 and SiH4 are introduced under vacuum, and the thickness of the SiN layer is 75-85nm.

[0045] As a preferred implementation, in the step 1, a nanoscale texture is formed on the front and back sides of the N-type silicon substrate.

[0046] As a preferred implementation, BCl 3 gas is introduced when boron diffusion is performed on the front side of the N-type silicon substrate in step 2.

[0047] The temperature generated by applying bias when the silicon nitride film is normally opened is about 600°C at -20V, and the battery cell can be laser sintered normally to form a good ohmic contact; the temperature generated by applying voltage when the silicon nitride film is not fully opened is about 8000°C at -20V, and the battery cell will be abnormally overburned at this temperature. Therefore, the silicon nitride film is fully opened by applying bias twice in the LECO process, thereby reducing the EL black edge problem caused by overburning. The present invention performs two processes in the LECO process. The first time, a bias of 3-10V and laser scanning are applied. Since the applied bias is relatively small, the temperature generated is relatively low, and the temperature generated by the first scan can be used to further open the silicon nitride film layer; the second time, a bias of 11-20V and laser scanning are applied to form a good ohmic contact. Since the silicon nitride film layer is further opened at the periphery, no ultra-high temperature is generated in the peripheral area, solving the black edge problem caused by overburning.

[0048] Example 1

[0049] A method for preparing a solar cell comprises the following steps:

[0050] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0051] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0052] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0053] Step 4: forming a 1.6 nm thick silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a 150 nm thick polysilicon layer on the silicon oxide layer, and forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0054] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 45Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0055] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0056] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 4.5 nm. On the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 78 nm by PECVD deposition.

[0057] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 80 nm is formed by PECVD deposition;

[0058] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0059] Step 10: Perform two LECO laser scans and apply reverse bias to further sinter and optimize the contact. The reverse bias voltage of the first LECO process is 3V, the reverse bias voltage of the second LECO process is 15V, and the laser power irradiated to the cell is 30%.

[0060] Example 2

[0061] A method for preparing a solar cell comprises the following steps:

[0062] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0063] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0064] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0065] Step 4: forming a silicon oxide layer with a thickness of 1 nm on the entire back surface of the N-type silicon substrate, and then growing a polysilicon layer with a thickness of 120 nm on the silicon oxide layer, and at the same time forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0066] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 53Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0067] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0068] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 5 nm. On the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 73 nm by PECVD deposition.

[0069] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 82 nm is formed by PECVD deposition;

[0070] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0071] Step 10: Further sintering and optimizing the contact by two LECO laser scans and reverse bias application, wherein the reverse bias voltage of the first LECO process is 5V, the reverse bias voltage of the second LECO process is 15V, and the laser power irradiated to the cell is 40%.

[0072] Example 3

[0073] A method for preparing a solar cell comprises the following steps:

[0074] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0075] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0076] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0077] Step 4: forming a 2.5 nm thick silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a 180 nm thick polysilicon layer on the silicon oxide layer, and forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0078] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 37Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0079] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0080] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 4 nm. On the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 83 nm by PECVD deposition.

[0081] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 75 nm is formed by PECVD deposition;

[0082] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0083] Step 10: Further sintering and optimizing the contact by two LECO laser scans and reverse bias application, wherein the reverse bias voltage of the first LECO process is 7V, the reverse bias voltage of the second LECO process is 15V, and the laser power irradiated to the cell is 10%.

[0084] Example 4

[0085] A method for preparing a solar cell comprises the following steps:

[0086] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0087] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0088] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0089] Step 4: forming a 2.1 nm thick silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a 160 nm thick polysilicon layer on the silicon oxide layer, and forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0090] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 53Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0091] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0092] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 4.3 nm. On the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 78 nm by PECVD deposition.

[0093] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 80 nm is formed by PECVD deposition;

[0094] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0095] Step 10: Further sintering and optimizing the contact by two LECO laser scans and reverse bias application, wherein the reverse bias voltage of the first LECO process is 10V, the reverse bias voltage of the second LECO process is 15V, and the laser power irradiated to the cell is 40%.

[0096] Example 5

[0097] A method for preparing a solar cell comprises the following steps:

[0098] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0099] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0100] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0101] Step 4: forming a 1.6 nm thick silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a 150 nm thick polysilicon layer on the silicon oxide layer, and forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0102] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 49Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0103] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0104] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 4.5 nm. On the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 78 nm by PECVD deposition.

[0105] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 80 nm is formed by PECVD deposition;

[0106] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0107] Step 10: Further sintering and optimizing the contact by two LECO laser scans and reverse bias application, wherein the reverse bias voltage of the first LECO process is 5V, the reverse bias voltage of the second LECO process is 11V, and the laser power irradiated to the cell is 30%.

[0108] Example 6

[0109] A method for preparing a solar cell comprises the following steps:

[0110] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0111] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0112] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0113] Step 4: forming a 1.6 nm thick silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a 150 nm thick polysilicon layer on the silicon oxide layer, and forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0114] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 49Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0115] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0116] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 4.5 nm. On the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 78 nm by PECVD deposition.

[0117] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 80 nm is formed by PECVD deposition;

[0118] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0119] Step 10: Further sintering and optimizing the contact by two LECO laser scans and reverse bias application, wherein the reverse bias voltage of the first LECO process is 5V, the reverse bias voltage of the second LECO process is 20V, and the laser power irradiated to the cell is 30%.

[0120] Comparative Example 1

[0121] A method for preparing a solar cell comprises the following steps:

[0122] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0123] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0124] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0125] Step 4: forming a 1.6 nm thick silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a 150 nm thick polysilicon layer on the silicon oxide layer, and forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0126] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 45Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0127] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0128] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 4.5 nm; on the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 78 nm by PECVD deposition;

[0129] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 80 nm is formed by PECVD deposition;

[0130] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0131] Step 10: Further sintering and optimizing the contact by LECO laser scanning and application of reverse bias voltage, wherein the reverse bias voltage of the LECO process is 20V and the laser power irradiated to the cell is 30%.

[0132] Comparative Example 2

[0133] The difference from Example 1 is that the two LECO laser scanning and reverse bias application in step 11 are changed to one time in this comparative example as follows:

[0134] A method for preparing a solar cell comprises the following steps:

[0135] Step 1: Texturing the N-type silicon substrate to form a nano-scale textured surface on the front and back sides of the N-type silicon substrate;

[0136] Step 2: BCl3 gas is introduced to perform boron diffusion doping on the front side of the N-type silicon substrate after texturing, so that a doped P+ layer and a borosilicate glass layer are formed on the front side of the N-type silicon substrate, and a borosilicate glass layer is formed on the back side of the N-type silicon substrate;

[0137] Step 3: removing the borosilicate glass layer on the back of the N-type silicon substrate by hydrofluoric acid pickling, and polishing the back of the N-type silicon substrate by sodium hydroxide solution to form a flat surface structure;

[0138] Step 4: forming a 1.6 nm thick silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a 150 nm thick polysilicon layer on the silicon oxide layer, and forming a polysilicon layer on the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0139] Step 5: Phosphorus is diffused into the polysilicon layer on the back of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer, wherein the square resistance of the N+ polysilicon layer is 45Ω, and an N+ polysilicon layer and a phosphorus silicon glass layer are formed on the front of the N-type silicon substrate;

[0140] Step 6: firstly, a roller-type chain hydrofluoric acid pickling method is used to remove the phosphosilicate glass layer on the front side of the N-type silicon substrate, and then a tank-type sodium hydroxide solution alkaline pickling method is used to remove the N+ polysilicon layer on the front side of the N-type silicon substrate, and finally, a tank-type hydrofluoric acid pickling method is used to remove the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side of the N-type silicon substrate;

[0141] Step 7: On the P+ layer on the front side of the N-type silicon substrate, water / TMA / N2 is introduced under vacuum at 300°C to deposit aluminum oxide by ALD to form an aluminum oxide layer with a thickness of 4.5 nm. On the aluminum oxide layer on the front side of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum to form a SiN layer with a thickness of about 78 nm by PECVD deposition.

[0142] Step 8: On the N+ polysilicon layer on the back of the N-type silicon substrate, NH3 and SiH4 are introduced under vacuum, and a SiN layer with a thickness of about 80 nm is formed by PECVD deposition;

[0143] Step 9: Electrode printing is performed on the front and back sides of the N-type silicon substrate, followed by sintering and light decay to form silver electrodes;

[0144] Step 10: Further sintering and optimizing the contact by LECO laser scanning and reverse bias application. The reverse bias voltage of the LECO process is 15V, and the laser power irradiated to the cell is 30%.

[0145] Comparative Example 3

[0146] The difference from Example 1 is that the two LECO laser scanning and reverse bias application in step 11 are changed to one time in this comparative example as follows:

[0147] Step 11: Further sintering and optimizing the contact by LECO laser scanning and application of reverse bias. The reverse bias voltage of the LECO process is 10V.

[0148] Comparative Example 4

[0149] The difference from Example 1 is that the two LECO laser scanning and reverse bias application in step 11 are changed to one time in this comparative example as follows:

[0150] Step 11: Further sintering and optimizing the contact by LECO laser scanning and reverse bias application. The reverse bias voltage of the LECO process is 5V.

[0151] Comparative Example 5

[0152] The difference from Example 1 is that the reverse bias voltages of the two LECO laser scans and the reverse bias voltage applied in step 11 are different, as follows:

[0153] Step 11: Further sintering and optimizing the contact by LECO laser scanning and reverse bias application. The reverse bias voltage of the first LECO process is 5V, and the reverse bias voltage of the second LECO process is 30V.

[0154] Comparative Example 6

[0155] The difference from Example 1 is that the two LECO laser scanning and reverse bias application in step 11 are changed to one time in this comparative example as follows:

[0156] Step 11: Further sintering and optimizing the contact by LECO laser scanning and application of reverse bias. The reverse bias voltage of the first LECO process is 15V, and the reverse bias voltage of the second LECO process is 15V.

[0157] Comparative Example 7

[0158] The difference from Example 1 is that the two LECO laser scanning and reverse bias application in step 11 are changed to one time in this comparative example as follows:

[0159] Step 11: Further sintering and optimizing the contact by LECO laser scanning and application of reverse bias. The reverse bias voltage of the first LECO process is 5V, and the reverse bias voltage of the second LECO process is 9V.

[0160] Comparative Example 8

[0161] The difference from Example 1 is that the two LECO laser scanning and reverse bias application in step 11 are changed to one time in this comparative example as follows:

[0162] Step 11: Further sintering and optimizing the contact by LECO laser scanning and reverse bias application. The reverse bias voltage of the first LECO process is 2V, and the reverse bias voltage of the second LECO process is 15V.

[0163] The N-type silicon wafers prepared in the above-mentioned embodiments 1-5 and comparative examples 1-6 were respectively used to detect their black edges, and their black edge ratios were calculated. The results are shown in Table 1.

[0164] Table 1

[0165]

[0166] Embodiments 1-6 are N-type silicon wafers prepared by the method of the present invention. Two LECO processes are set up during production, wherein the reverse bias voltage applied for the first time is 3-10V, and the reverse bias voltage applied for the second time is 11-20V. The average black edge ratio of the prepared N-type silicon wafers is 0.785%, which is 2.215% lower than the conventional 3% in the prior art. The reduction ratio of the black edge is reduced by 73.8% on the original basis, which has a very large improvement on the black edge rate of conventionally produced N-type silicon wafers and lays a good foundation for the subsequent application of solar cells.

[0167] Comparative Examples 1-4 are N-type silicon wafers prepared by the method of the present invention. Only one LECO process is set during production. The average black edge ratio of the N-type silicon wafers obtained under the process limit is 1.642%; in Comparative Examples 5-8, although the LECO process is set twice in the process steps, when the reverse bias set during production is higher or lower than the limited reverse bias value or the reverse bias of only one LECO process is within the limited range, the average black edge ratio of the N-type silicon wafers obtained is 1.17%, which is higher than the average black edge ratio of 0.785% of the N-type silicon wafers obtained in Examples 1-6.

[0168] On the whole, the average black edge ratio of the N-type silicon wafers prepared by the present invention is 0.785%, which is much smaller than the average black edge ratio of the N-type silicon wafers prepared by comparative examples 1-8, which is 1.406%, and the effective improvement rate of the black edge ratio is 44.17%.

[0169] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a solar cell, characterized in that: The steps include: Step 1: Select an N-type silicon substrate and perform double-sided texturing; Step 2: Diffuse boron on the front side of the silicon substrate to form a P+ doping layer and a borosilicate glass layer on the front side and a borosilicate glass layer on the back side; Step 3, removing the borosilicate glass layer on the back side of the N-type silicon substrate, and performing alkali cleaning and polishing on the back side of the N-type silicon substrate; Step 4: forming a silicon oxide layer on the entire back surface of the N-type silicon substrate, and then growing a polysilicon layer on the silicon oxide layer, and at the same time forming a polysilicon layer on the borosilicate glass layer on the front surface; Step 5: Phosphorus is diffused into the polysilicon layer on the back side of the N-type silicon substrate to form an N+ polysilicon layer and a phosphorus silicon glass layer on the back side and an N+ polysilicon layer and a phosphorus silicon glass layer on the front side; Step 6: remove the phosphosilicate glass layer, the N+ polysilicon layer, the borosilicate glass layer on the front side of the N-type silicon substrate and the phosphosilicate glass layer on the back side; Step 7: depositing a front passivation layer and a front anti-reflection layer in sequence on the P+ doped layer on the front side of the N-type silicon substrate; Step 8, depositing a back anti-reflection layer on the N+ polysilicon layer on the back side of the N-type silicon substrate; Step 9: Electrodes are printed on the front and back of the N-type silicon substrate, and then sintered and light decayed to form metal electrodes; Step 10: Perform two LECO processes to further sinter and optimize the contact. The reverse bias voltage applied in the first LECO process is 3-10V, and the reverse bias voltage applied in the second LECO process is 11-20V.

2. The method for preparing a solar cell according to claim 1, characterized in that: In the step 10, the laser power irradiated on the battery cell is 10%-40%.

3. The method for preparing a solar cell according to claim 1, characterized in that: In step 4, the thickness of the silicon oxide layer is 1-2.5 nm, and the thickness of the polysilicon layer is 120-180 nm.

4. The method for preparing a solar cell according to claim 3, characterized in that: In the step 5, the sheet resistance of the N+ polysilicon layer is 37-53Ω.

5. The method for preparing a solar cell according to claim 3, characterized in that: The thickness of the passivation layer in step seven is 4-5 nm.

6. The method for preparing a solar cell according to claim 3, characterized in that: In the step 7, NH3 and SiH4 are introduced under vacuum conditions, and the thickness of the anti-reflection layer is 73-83 nm.

7. The method for preparing a solar cell according to claim 1, characterized in that: In step eight, NH3 and SiH4 are introduced under vacuum, and the thickness of the anti-reflection layer is 75-85nm.

8. The method for preparing a solar cell according to claim 1, characterized in that: In the step 1, a nanoscale texture is formed on the front and back sides of the N-type silicon substrate.

9. The method for preparing a solar cell according to claim 1, characterized in that: In the step 2, BCl3 gas is introduced when boron is diffused and doped on the front side of the N-type silicon substrate.

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